1. Field of the Invention
This invention relates to interference of electron waves and processing interference current, and, more particularly to a quantum interference device (QID) and a method for converting signals carried by a magnetic field, an electric field, light or the like to electric signals by the Aharohov-Bohm effect (A-B effect), the optical Stark effect or the like.
2. Related Background Art
There has been developed a photodetector without photon absorption as shown in FIG. 1A which is a kind of QID. This device is operated as follows.
Electrons injected from a source electrode 110 disposed at the left side of FIG. 1A begin to propagate through paths or waveguides 111, 112 and 113 towards a drain electrode 114 formed at the right side with a wave function and an energy E indicated by EQU e.sup.ikx .phi..sub.S (z)Y(y) (1) EQU E=(h.sup.2 /2m*)k.sup.2 +E.sub.S +E.sub.Y ( 2).
The paths 111, 112 and 113 are formed with a quantum well structure (QWS), a quantum line structure (QLS) or the like. In the formulae (1) and (2), m* is the effective mass of an electron moving in an x-direction, k is an angular wave number of the motion in the x-direction, E.sub.S and .phi..sub.S (Z) are respectively the energy and the wave function of a ground state level of electron subbands with respect to a z-direction, and E.sub.Y and Y(y) are respectively the energy and the wave functions of a ground state level of electron subbands with respect to a y-direction.
As shown in the band structures of FIGS. 1B-1D, the wave function of electrons is split in two in a central part, and in the upper QLS 112 (narrow one) the wave function and the energy are as indicated in formulae (3) and (4), respectively, while in the lower QLS 13 (wide one) they are as indicated in formulae (5) and (6), respectively. EQU e.sup.ikNx .phi..sub.Na (z)Y(y) (3) EQU E=(h.sup.2 /2m*)k.sub.N +E.sub.Na +E.sub.Y ( 4) EQU e.sup.ikWx .phi..sub.Wa (z)Y(y) (5) EQU E=(h.sup.2 /2m*)k.sub.W +E.sub.Wa +E.sub.Y ( 6)
In the formulae (3) and (5), normalization constants are omitted, and in those formulae (3)-(6), E.sub.Na and .phi..sub.Na (z) are respectively the energy and the wave function of a ground state level of electron subbands in the upper QLS 112 with respect to the z-direction, E.sub.Wa and .phi..sub.Wa (z) are respectively the energy and the wave function of a ground state level of electron subbands in the lower QLS 113 with respect to the z-direction, and k.sub.N and k.sub.W are respectively the angular wave numbers of the motion in the x-direction in upper and lower QLS's 112 and 113.
Since, in general, a relation E.sub.Na .apprxeq.E.sub.S is satisfied, k.sub.N .apprxeq.k is obtained from the formulae (2) and (4), and likewise k.sub.W .apprxeq.k is obtained in the lower QLS 113. In this example, however, k.sub.W =k.sub.N is established because this device is formed such that E.sub.Na =E.sub.Wa is established when no light is applied to the central part (i.e., electrons are branched into the upper and lower QLS's 112 and 113 in an equal ratio).
Here, if light is passed through the central part of this device, the following optical Stark shift occurs. EQU E.sub.Na .fwdarw.E.sub.Na -(e.mu..sub.N .epsilon.).sup.2 /.delta..sub.N( 7) EQU E.sub.Wa .fwdarw.E.sub.Wa -(e.mu..sub.W .epsilon.).sup.2 /.delta..sub.W( 8)
where ##EQU1## and E.sub.Nb and E.sub.Wb are respectively energies of the second level in the upper and lower QLS's 112 and 113 with respect to the z-direction and .mu..sub.N and .mu..sub.W are respectively magnitudes of dipoles of a transition from the ground state level to the second level in the upper and lower QLS's 112 and 113.
It is especially effective when the device is designed such that following relation is satisfied (see the band structure in FIG. 1C). EQU E.sub.Wb -E.sub.Wa &lt;h.omega.&lt;E.sub.Nb -E.sub.Na ( 10)
Hence, .delta..sub.N &gt;0 and .delta..sub.W &lt;0, so E.sub.Na in the upper path 112 shifts to the lower value and E.sub.Wa in the lower path 113 shifts to the upper value as is seen in the formulae (7) and (8) (see the hatched arrows in the band structure of FIG. 1C). Then, k.sub.N of the upper path 112 increases while k.sub.W of the lower path 13 decreases, as is known from the formulae (4) and (6).
Thus, if the wave numbers in the upper and lower QLS's 112 and 113 are different, a phase difference between electrons travelling in the upper QLS 112 and electrons travelling in the lower QLS 113 occurs after they have traveled in each path QLS 112 and 113 the same distance in the x-direction. As the part where the light is applied is 0.ltoreq.x.ltoreq.L, the phase difference .DELTA..theta. is given by ##EQU2##
For instance, if the phase difference .DELTA..theta. is .pi., the form of a combined wave function will become .phi..sub.A that corresponds to the second state, but not .phi..sub.S that corresponds to the first state, of the combined wave, when the wave function of electrons is over again combined at the right side path 111 in FIG. 1A. However, the combined wave has only an energy corresponding to .phi..sub.S but not .phi..sub.A, so this is reflected backward. Hence, electrons cannot reach the drain electrode 114 on the right side, so that current would not flow between the source electrode 110 and the drain electrode 114. In fact, as is seen from the formulae (7), (8), (11) and so forth, the phase difference .DELTA..theta. varies in accordance with the intensity I (associated with .epsilon..sup.2) of the light, and the transmittance or transmission coefficient of current to the drain electrode 114 on the right side varies in proportion to cos.sup.2 (.DELTA..theta./2). Thus, the current J is given by EQU J=J.sub.o cos.sup.2 (.DELTA..theta./2) (12)
where J.sub.o is a constant.
Therefore, .DELTA..theta. is obtained from a measured value of J by using the formula (11), and the intensity I of the light is known from the relationship between .DELTA..theta. and the intensity I, for example, EQU .DELTA..theta.=gI+.DELTA..theta..sub.o ( 13)
where g and .DELTA..theta..sub.o are constants, respectively.
The above technology is disclosed in the Japanese patent application No. 2-45085 filed by the same assignee.
However, according to the above technology, there may be a problem that an error occurs when the intensity I of light is derived from the current value J. In other words, the measured value of J would fluctuate for the same intensity I of light, each time its value is measured.
This is because the flow of current would fluctuate even if it were highly controlled, due to the collision of electrons at a microscopic level, the capture of electrons to a certain energy level, etc., and because J.sub.o in the formula (12) would waver depending on time. Further, where no current is detected at the side of the drain electrode 114, confirmation could not be made if there really exists no current or no current is detected because electrons have been reflected backward.
In such manner, errors would occur where the phase difference .DELTA..theta. is estimated from the measured current value J, owing to an uncertainty of J.sub.o.